Researchers found that of the three teas, the polysaccharides in black tea had the most glucose-inhibiting properties. The black tea polysaccharides also showed the highest scavenging effect on free radicals, which are involved in the onset of diseases such as cancer and rheumatoid arthritis.
Next to water, tea is the second most consumed beverage in the world. Researchers from the Tianjin Key Laboratory in China studied the polysaccharide levels of green, oolong and black teas and whether they could be used to treat diabetes. Polysaccharides, a type of carbohydrate that includes starch and cellulose, may benefit people with diabetes because they help retard absorption of glucose.
The researchers found that of the three teas, the polysaccharides in black tea had the most glucose-inhibiting properties. The black tea polysaccharides also showed the highest scavenging effect on free radicals, which are involved in the onset of diseases such as cancer and rheumatoid arthritis.
“Many efforts have been made to search for effective glucose inhibitors from natural materials,” says lead researcher Haixia Chen. “There is a potential for exploitation of black tea polysaccharide in managing diabetes.”
The possible beneficial health effects of tea consumption have been suggested and supported by some studies, but others have not found beneficial effects.
Studies claim that the polyphenol content of green tea has antioxidant properties that can help prevent cancer, however research is ongoing.
There is also a suggestion that it can increase endurance in exercise by improving fat metabolism.
One should consult a doctor before using high concentrations of tea for disease prevention.
Ingestion of large amounts of tea may cause nutritional and other problems because of the strong binding activities of tea polyphenols and the caffeine content, although no solid data exist concerning harmful effects of tea consumption.
An herbal tea, tisane, or ptisan is an herbal infusion not made from the leaves of the tea bush.
Tisanes can be made with fresh or dried flowers, leaves, seeds or roots, generally by pouring boiling water over the plant parts and letting them steep for a few minutes.
There are many varieties of herbal tea.
Among the rarest and most expensive varieties of tea, white tea is produced almost exclusively in China. It belongs to the same species (Camellia sinensis) as other tea plants, but has a higher proportion of buds to leaves. The buds are covered by silvery hairs, giving the plant a whitish appearance.
Some teas are processed more than others. White tea is rapidly steamed and dried, leaving the leaves virtually “fresh.” Green tea, composed of mainly leaves, is steamed or fired prior to being rolled. Oolong and black teas get their dark color and flavor from additional processing.
The researchers theorize that processing may play a part in tea’s cancer-fighting potential. The key is a class of chemicals called polyphenols.
“Many of the more potent tea polyphenols (‘catechins’) become oxidized or destroyed as green tea is further processed into oolong and black teas,” says Roderick H. Dashwood, Ph.D., a biochemist in the university’s Linus Pauling Institute and principal investigator of the study. “Our theory was that white tea might have equivalent or higher levels of these polyphenols than green tea, and thus be more beneficial.”
Chemical analysis confirmed their theory. White tea contains the same types of polyphenols as green tea, but in different proportions. Those present in greater amounts may be responsible for white tea’s enhanced cancer-fighting potential, says Dashwood.
Encouraged by reports of cancer-fighting chemicals in green tea, the researchers decided to test white tea to determine whether it has similar qualities. They brewed four varieties of white tea and subjected each to a laboratory test using bacteria. The test, called the Salmonella assay, determines whether a chemical can cause or prevent DNA mutations, the earliest steps leading to cancer.
White tea inhibited mutations more efficiently than green tea. This means it may have more potential to prevent cancer than green tea, says Gilberto Santana-Rios, Ph.D., a post-doctoral research associate with the institute, located in Corvallis, Ore.
The researchers, now performing experiments in rats, report that their latest data indicate that white tea may protect against colon cancer in particular. They attribute this to elevated levels of particular liver enzymes.
The researchers say more studies are needed to determine whether white tea actually protects people against cancer.
“White tea, and tea in general, is a healthy alternative to other popular drinks, such as sodas,” says Dashwood. “But to be on the safe side, one should maintain a healthy lifestyle that includes a diet rich in fruits and vegetables, regular exercise, and avoidance of smoking.”
Black, oolong, green or white teas have a common origin. Each is produced from the leaves of the Camellia sinensis bush. The leaves are loaded with flavonoids and other polyphenols that work as antioxidants, possibly lowering the risk of some diseases.
While numerous studies have found possible benefits, the actual benefits of drinking tea are not certain. Most research about tea’s benefits is based on population (epidemiological) studies. Findings are limited because factors other than tea consumption could influence the results. Here’s some of what’s known about tea’s potential benefits:
Cardiovascular
It’s still uncertain if drinking tea over long periods might positively affect cholesterol levels, blood pressure and atherosclerosis. There’s some early evidence that regularly drinking green tea may reduce heart attack risk or atherosclerosis. There’s conflicting evidence on black tea consumption and heart attack risk reduction.
Cancer
It’s still unknown whether regular black tea consumption influences cancer rates. Early lab tests with white tea indicate it may protect against colon cancer in particular. So far, well-designed studies haven’t proven this.
Bone and joint health
Early laboratory research indicates green tea could be beneficial in reducing inflammation related to arthritis and slowing cartilage breakdown. Some early data indicate that regular tea consumption might improve bone mineral density in older women.
Memory
Studies are limited, but a recent one found that older adults in Japan who drank green tea daily showed less risk of memory difficulty, compared with those who didn’t drink tea regularly.
While there’s still much to learn about tea’s health benefits, the potential benefits seem to be in the cup, not in supplements or tea extract capsules. So far, there’s no certainty that the compounds in supplements are the same ones in tea, and even less certainty that these supplements might provide the same potential health benefits as tea.
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